What Is AGP (Accelerated Graphics Port)? Meaning, Characteristics, Uses, and Benefits
AGP refers to a video standard used to process graphics on computers.
- Accelerated Graphics Port (AGP) is defined as a hardware interface designed to connect a graphics card, video card, or 3D accelerator to a computer system to speed up 3D video output.
- This article explains the fundamentals of AGP, its key characteristics, uses, and advantages.
Table of Contents
What Is AGP?
Accelerated Graphics Port (AGP) is a hardware interface designed to connect a graphics card, video card, or 3D accelerator to a computer system to speed up 3D video output. The card standard was introduced by Intel in 1997 as a replacement for the older Peripheral Component Interconnect (PCI) interface.
Typically, PCI graphics cards are known to receive data in ‘groups,’ which are later used to create a graphical image. For example, while projecting an image on a system, the PCI card would receive length, width, and height at different intervals. Upon data reception, it would aggregate all this data to present the whole image finally. However, AGP cards receive all the image data at once. As a result, it produces sharper and smoother graphics in a quick time.
Moreover, the AGP interface uses a dedicated bus to control the movement of graphical data implying that AGP supports direct line communication to the CPU and RAM. As a result, it renders graphics much faster than the previous PCI standards.
AGP expansion slots are located near the processor on the computer’s motherboard, much like PCI slots. Their form factor, too, resembles that of their PCI counterparts. Owing to its demand and utility, in 1998, AGP Pro was introduced as an extension of the AGP interface. It was typically designed for powerful workstations that would accomplish power-intensive tasks, much like advanced graphical programs. The new specification had bigger slots and more voltage pins for video cards. AGP Pro showed backward compatibility with earlier AGP versions.
The point-to-point AGP technology was popular when desktop computers were in demand. However, it was later replaced by high-speed PCI Express (PCIe) in 2004. Hence, most desktop machines manufactured after 2010 lack the AGP slot.
AGP versions
AGP port has several slot specifications, such as AGP 1.0, 2.0, and 3.0. All AGP cards need to be compatible with these AGP slots. Some common AGP versions include:]
1. AGP 1.0
The interface AGP 1.0 has the following technical specifications:
- Clock speed: 66 MHz
- Voltage: 3.3 V
- Speed: 1X and 2X
- Transfer rate: 266 MB/s to 533 MB/s
2. AGP 2.0
The technical specifications of AGP 2.0 include the following:
- Clock speed: 66 MHz
- Voltage: 1.5 V
- Speed: 4X
- Transfer rate: 1,066 MB/s
3. AGP 3.0
The specifications of AGP 3.0 include the following:
- Clock speed: 66 MHz
- Voltage: 0.8 V
- Speed: 8X
- Transfer rate: 2,133 MB/s
In the above data, the transfer rate refers to bandwidth measured in megabytes. Moreover, speed of 1X, 2X, 4X, and 8X refers to the bandwidth speed where X is equal to the speed of AGP 1.0 (i.e., 266 MB/s). For example, the speed 8X of AGP 3.0 implies the bandwidth speed of 8 x speed of AGP 1.0.
To add to these, Microsoft released the next version of AGP in the name of AGP 3.5 Universal Accelerated Graphics Port (UAGP). Its specifications are similar to that of AGP 3.0.
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Characteristics of AGP
Apart from high-definition graphics throughput, the brown-colored AGP port reveals several other key features. Let’s understand some of the vital characteristics of AGP in detail.
1. Pipelining
In computer architecture, AGP slots are enabled with pipelining features allowing them to receive and process multiple instructions simultaneously during a bus or memory access. On the other hand, PCI lacks this capability, implying it can only receive one instruction at a time. It cannot make another data request until the first data is transferred. Thus, AGP has a better data transfer rate than any previously known standards.
2. Sideband addressing
Typically, when a video card sends graphical data to the CPU for processing purposes, it sends a set of addresses in each packet along with the video data to ensure that the right data is retrieved and processed. However, checking each data packet for addresses before processing can slow down a computer, affecting systems speed and performance.
Sideband addressing is a method that resolves the above issue by sending addresses on eight additional data lines. This arrangement ensures that the addresses are found and read faster, elevating the overall system performance. The feature is particularly useful for rendering 3D graphics quickly and efficiently. AGP video cards were the first to implement the sideband addressing feature.
3.Texture storage
Under the AGP premise, the graphics controller has direct access to the system’s main memory. In previous PCI graphic cards, it was essential to first load a texture from the system’s RAM to the card’s memory to read the data appropriately. However, AGP cards have the facility to read textures directly from the system’s RAM using Graphics Address Remapping Table (GART). The GART is known to allocate main memory for texture storage directly accessed by the video card.
With the addition of memory to graphics cards, AGP ensured that it could access large textures that could not previously fit into the graphics card’s local memory. Earlier, the texture had to be moved to local memory over the PCI bus. This required other information to be moved out of local memory to make space for new data.
The entire process is eliminated by AGP as it allows texture storage in the system’s memory, where the AGP graphics card can directly execute it. The ability to execute textures from a system’s memory is called Direct Memory Execute (DIME). DIME, along with the dynamic memory allocation mechanism, allows frequently used textures to live on a graphic card’s local memory, thereby boosting overall performance.
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Uses of AGP
AGP standard is typically designed to render smooth 3D images on regular computers. Such good-quality graphics on a normal PC gives you the experience of working on a high-end dedicated graphics terminal. AGP generates the finest visuals by using the system’s resources better.
Let’s understand some of the key uses of AGP.
1. Perform complex 3D calculations
AGP slots are specifically designed for graphics cards. The CPU has to perform complex 3D calculations to create 3D images. The graphics controller is known to access texture data and bitmaps to create the final images. However, in the process, the controller tends to read different texture elements and average them to create one on-screen pixel.
The created pixels are required to be stored in the memory buffer until all the calculations are performed. As the textures are quite large, they cannot be stored in the video card’s memory. Thanks to AGP, the texture data is stored in the system’s main memory. Thus, to render high-definition video data, it is recommended that the system has a large enough memory.
2. Enable new class of applications
AGP is typically useful for 3D games and videos. It also enables the development of new classes of PC programs (or applications) like 3D CAD/CAM, 3D UI, and data visualization that are used across fields like architecture, machining, engineering, computer simulations, and several others.
AGP is known to provide quicker throughput when compared to PCI. This speed is crucial for 3D graphics rendering, high-definition games, and graphics for engineering and architecture.
AGP port connects the video card, computer’s processor, and memory. Due to this connection, you can play video games that reveal faster load times and have better graphics. Moreover, AGP also allows the creation of high-resolution video images using graphic card processors.
3. Support split transactions
AGP lends support to split transactions, wherein the address and data buses remain separated. As a result, the address phase refrains from using the main address/data (AD) line. Thus, the graphics card can send multiple addresses and data phases to the host to allow ordered processing of data. This avoids long delays, which generally occur due to the bus staying idle during data read operations.
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Advantages of AGP
AGP refers to a specific bus specification that adds advanced graphics capabilities to personal computers. It has several advantages when compared to traditional PCI standards. Let’s look at some of the factors that make AGP unique..
AGP Advantages
1. Higher bandwidth support
AGPs rely on key methods like sideband addressing, pipelining, and high-speed data transfers per clock to achieve peak bandwidths. Moreover, it aids in directly implementing texture features from the main memory (DIME), implying that the requirement to pre-load data into the local system is reduced. All these features contribute to the bandwidth support that is 4X higher than the PCI bus.
Technically, the PCI bus has a transfer rate of 133 MB/s, while AGP reveals a transfer rate of approximately 533 MB/sec at 66 MHz clock speed.
2. Reduced congestion
Typical PCI application serves several peripheral devices like LAN chips, video capture systems, and disk controllers. However, AGP operates independently of most PCI transactions. As a result, there is reduced contention between CPU and I/O devices for memory and bus access.
Moreover, the CPU can concurrently access the system RAM and AGP RAM of the graphic chip. This is possible due to the well-known paradigm of out-of-order execution and queuing hardware support in the chipset. Hence, despite large access requests to the graphics chip, there is no CPU degradation.
3. Enhanced 3D graphics
AGP provides dedicated point-to-point communication between the graphics subsystem and the core-logic chipset via a bus. With this direct connection to the CPU and system memory, AGP enables your computer to collect the necessary information quickly and efficiently to render complex 3D graphics that run at higher clock speeds.
4. Compatibility and flexibility
For AGP, compatibility exists on various levels. The speed of AGP is always backward compatible while signaling voltages are not. Moreover, as AGP slots and connectors are keyed, one should only prefer electrically compatible equipment.
Typically, AGP cards showcase selective forward and backward compatibility. For example, 1.5V cards may not fit into the 3.3V slots and vice versa. Similarly, AGP cards work with AGP Pro slots, but AGP Pro cards do not fit into standard AGP slots.
5. Isolated video subsystem
AGP typically isolates the video system from the rest of the computer. As a result, graphic devices do not compete for additional I/O bandwidth, unlike PCI. Also, as the video card is removed from the PCI bus, it benefits other PCI devices as they do not compete for more bandwidth.
6. Faster memory access
AGP adds an extra port to the graphics chip that speeds up memory access. It allows the CPU to concurrently read textures from AGP memory and read/write Z-values and pixels from the system’s local memory. Also, when the CPU needs to provide graphics information by giving commands or animated textures during 3D rendering, AGP allows the CPU to write to shared system AGP memory directly. This is much faster than accessing memory via the PCI bus while executing graphics-related commands.
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Takeaway
AGP replaced older PCI connections to bring faster and better graphics to computer systems. Application software related to 3D graphics can process videos and graphical information effectively by exploiting functionalities of AGP that are key to efficient memory allocation and management. AGP applications allow users to watch higher screen resolutions at higher frame rates and have more textures.
However, as AGP technology is phasing out, it will eventually be replaced by faster and more efficient buses and interfaces in the coming years.
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